1. Field of the Invention
This invention relates to cable television (CATV) networks and services. More particularly, the invention relates to an in-band traffic routing system for a CATV communication system.
2. Description of the Related Art
CATV network operators have begun to offer their subscribers an increasingly diverse array of services from which to choose. In addition to the more “traditional” services that are offered, such as broadcast and premium video entertainment services, settop terminals are capable of handling interactive data and services.
The CATV transmission spectrum 21, as shown in FIG. 1, typically extends up to one gigahertz (1 GHz). In order to provide a bidirectional communication flow over the cable transmission network between the headend and the settop terminals, the transmission spectrum 21 is divided into upstream and downstream bandwidths 26, 28. The upstream bandwidth 26 is utilized to send communications from a settop terminal to the headend. The downstream bandwidth 28 is for communications from the headend to the settop terminals. The upstream bandwidth 26 includes frequencies from five to fifty megahertz, and typically includes a plurality of upstream communication channels 37. The downstream bandwidth 28 includes frequencies above fifty megahertz, and is further divided into a plurality of “in-band” channels 32, each having a bandwidth of 6 MHZ. The in-band channels 32 are primarily used for transmission of analog or digital video broadcasts and their associated analog or digital audio programs. Data channels 33, which typically have a much smaller bandwidth than in-band channels 32, are interspersed throughout the upstream bandwidth 26 and are used to transmit all other downstream communications. A separate control data channel (CDC) 34 is provided as a fixed data channel for facilitating administrative functions.
When an interactive communication is desired by the user of a settop terminal, the downstream communication path is established on one of the downstream data channels 33, 34. The upstream communication path is established on one of the upstream communication channels 37 or via the local telecommunication (telco) network. The drawback with this type of arrangement is that a settop terminal must have two separate receivers: 1) a tuner for receiving the in-band channels 32; and 2) an out-of-band data receiver for receiving the data channels 33, 34. This increases the cost and complexity of the settop terminal.
One alternative for eliminating the need for a separate data receiver is to send the data within the in-band channels 32. However, a significant problem in establishing communications between a headend and a settop terminal in this manner is that the downstream communication path is almost randomly dynamic. Since the downstream communication path is dependent upon the in-band channel 32 that a subscriber selects, it is impossible to predict when a change to a different in-band channel 32 will be made, or to which in-band channel 32 the tuner will be tuned. If a communication session using an in-band channel 32 is initially established, the subscriber must not change in-band channels 32 during the duration of the session or the downstream communication path will be lost, thereby interrupting the session. This is unacceptable for data-critical applications.
An alternative for eliminating the data receiver is to replicate the out-of-band data stream on each in-band channel 32. In this manner, the out-of-band data stream is available for every in-band channel 32 that the subscriber chooses. However, this approach is inherently wasteful of the bandwidth if the data is only required for a single settop terminal, such as for an interactive communication.
Accordingly, there exists a need for a system which conservatively utilizes the available communication bandwidth and does not require two separate receivers.